When a variant is renamed to a name that is not a valid properties
formula, rename-shape-or-variant passed an empty map as the updated
properties. The variant functions now assert that properties are a
vector or nil, so the rename failed. Pass an empty vector instead,
which means the same and keeps the order the properties have.
Add a test that renames a variant to an invalid name through a test
store and checks that it gets marked with :variant-error.
AI-assisted-by: claude-opus-5-5
c034838a42